Android JNI support for speaker diarization (#1421)

sherpa-onnx/jni/voice-activity-detector.cc

@@ -71,10 +71,12 @@ JNIEXPORT jlong JNICALL Java_com_k2fsa_sherpa_onnx_Vad_newFromAsset(
   AAssetManager *mgr = AAssetManager_fromJava(env, asset_manager);
   if (!mgr) {
     SHERPA_ONNX_LOGE("Failed to get asset manager: %p", mgr);
+    return 0;
   }
 #endif
   auto config = sherpa_onnx::GetVadModelConfig(env, _config);
   SHERPA_ONNX_LOGE("config:\n%s", config.ToString().c_str());
+
   auto model = new sherpa_onnx::VoiceActivityDetector(
 #if __ANDROID_API__ >= 9
       mgr,